A crimping die for niobium-tin superconducting joint

Abstract

A crimping die for a niobium-tin superconducting joint has a circular base with a boss in the center and a pin hole on the side of the boss. The outer cylinder of the mold is mounted on the base, and the inner wall of the outer cylinder of the mold is fitted and fixed to the outer side of the boss of the base. There is a pin hole on the side of the bottom of the outer cylinder, and the outer cylinder is fixed to the base by a pin. The outer cylinder is mounted outside the center cylinder, and the mandrel is located in the center of the center cylinder. The center cylinder is in a three-petal shape, and the three petals are spliced ​​into a cylindrical shape. The mandrel is a T-shaped structure, and the mandrel is positioned and matched with the three petals of the center cylinder through positioning grooves. The upper cover is on the upper part of the outer cylinder of the mold, and the inner side of the upper cover is threaded, which is matched with the upper edge of the outer cylinder of the mold through threads, so that the upper cover pushes the mandrel to move downward. The upper cover is located directly above the mandrel. During the downward rotation of the upper cover, the lower end surface of the top of the upper cover contacts the top surface of the mandrel, pushing the mandrel to move downward, pressing the niobium-tin superconducting wire and the metal powder in the center cylinder into one body, and the pressure of the joint part is uniform, and there is no damage to the niobium-tin superconducting connection.

Description

Technical Field

[0001] The invention relates to a crimping die for a niobium-tin superconducting joint. Background Art

[0002] Superconducting magnets that can generate strong magnetic fields are an important application of superconducting technology. For example, nuclear magnetic resonance spectrometers and magnetic resonance imaging require superconducting magnets to provide background magnetic fields. The intermetallic compound-based superconducting material niobium tin (Nb3Sn) is a commonly used low-temperature superconducting material with a high upper critical magnetic field and critical current density. The superconducting transition temperature is 18.3K, the upper critical magnetic field can reach 25T at 4.2K, and the critical current density carried under a magnetic field of 4.2K / 10T is about 5×10 5 A / cm 2 NbSn superconductor is one of the most ideal low-temperature superconducting materials for making high-field superconducting magnets above 10T.

[0003] NbSn superconductors have a typical A15 structure. NbSn superconducting magnets require that non-superconducting wires be wound into magnets first, and then undergo high-temperature diffusion heat treatment to generate NbSn phases with superconducting properties. After the NbSn superconductor is formed, it has poor plasticity and strong brittleness, making it difficult to operate mechanically. Therefore, it must first be operated before heat treatment.

[0004] The niobium-tin joint is the key to the niobium-tin superconducting magnet, and the quality of the joint directly affects the performance of the entire niobium-tin superconducting magnet. During the cooling and power-on process, the niobium-tin superconducting joint is the vulnerable point of the entire magnet system.

[0005] The joint resistance of the currently prepared Nb3Sn superconducting joint is relatively large. For example, the University of Washington in the United States uses chemical vapor deposition to prepare Nb3Sn superconducting joints. The preparation method disclosed in patent CN201010221920.8 requires the deposition of a Cu-Sn alloy coating first, which is complex and has poor operability. Summary of the invention

[0006] The purpose of the present invention is to overcome the shortcomings of the existing niobium tin joint preparation process being complex and having high resistance, and to provide a niobium tin superconducting joint crimping die. The present invention is used to prepare niobium tin superconducting joints, the process is simple and reliable, and a low-resistance Nb3Sn superconducting joint can be obtained.

[0007] The purpose of the present invention is achieved through the following technical solutions.

[0008] A crimping die for a niobium-tin superconducting joint is a cylindrical structure, comprising a base, a die outer cylinder, a center cylinder, a mandrel and an upper cover, wherein the base, the die outer cylinder, the center cylinder, the mandrel and the upper cover are coaxial. The base is circular, with a boss in the center and a pin hole on the side of the boss. The die outer cylinder is sleeved on the base, and the inner wall of the die outer cylinder and the outer side of the boss of the base are fitted and fixed. There is a pin hole on the side of the bottom of the outer cylinder, and the outer cylinder is fixed to the base by a pin. The outer cylinder is sleeved outside the center cylinder, and the mandrel is located in the center of the center cylinder. The upper cover is on the upper part of the die outer cylinder, and the inner side of the upper cover has a thread, which is threaded with the upper edge of the die outer cylinder, and the pitch of the thread is 0.5mm-1.5mm. The upper cover pushes the mandrel downward through threaded cooperation. A through hole is opened in the center of the upper cover for the entry and exit of niobium-tin superconducting wires. The upper cover is located directly above the core shaft. When the upper cover rotates downward, the lower end surface of the top of the upper cover contacts the top surface of the core shaft, pushing the core shaft to move vertically downward.

[0009] The mandrel is a T-shaped structure, with a wire groove on the top surface, and a positioning block on one side of the cylindrical surface below the top surface.

[0010] The central tube is a hollow cylinder formed by splicing three petals. A wire groove is opened on the inner wall of the first petal and the inner wall of the second petal of the three petals. The cross-section of the wire groove is circular. The radius of the wire groove is larger than the radius of the niobium tin superconducting wire, and the depth of the wire groove is equal to the height of the first petal. The niobium tin superconducting wire passes through the wire groove to prevent damage to the niobium tin superconducting wire when it is subjected to force. There is a positioning groove in the middle of the inner wall of the third petal, and the positioning block on one side of the core shaft is inserted into this positioning groove for positioning and guiding the core shaft. There is a positioning block in the middle position of the outer wall of the third petal, and the positioning block is inserted into the positioning groove on the inner wall of the outer tube of the mold, and cooperates with the positioning groove on the inner wall of the outer tube to prevent relative movement between the central tube and the outer tube.

[0011] The base is fixed horizontally, the upper cover is rotated, and the threaded joint of the upper cover and the outer tube is used to move the upper cover downward, pushing the mandrel below the upper cover to move vertically downward. During the movement, the positioning block on the side of the mandrel is inserted into the positioning groove of the center tube to ensure the linear movement of the mandrel without rotation. The lower end of the mandrel gradually presses the mixed powder of Nb powder and Sn powder in the center tube, so that the Nb wire at the bottom of the niobium-tin superconducting wire is pressed into one with the mixed powder of Nb powder and Sn powder.

[0012] The working process of the crimping die of the present invention for crimping the niobium-tin superconducting joint is as follows:

[0013] (1) Wind a superconducting wire into one or more turns, align the two ends of the superconducting wire side by side as the inlet and outlet ends. Use nitric acid to corrode the copper layer at the inlet and outlet ends of the Nb3Sn superconducting wire, with the corrosion section length of 0.5cm-10cm, exposing the Nb multifilaments and support core in the Nb3Sn wire, and remove the support core;

[0014] (2) Mixing Nb powder and Sn powder and then ball milling for 5 h to 20 h;

[0015] (3) Insert the two ends of the niobium-tin superconducting wire vertically into the center tube through the wire grooves of the first and second lobes on both sides of the center tube, respectively. The uncorroded part of the niobium-tin superconducting wire reaches the upper surface of the base boss, and the Nb multifilament enters the center tube. Pour the ball-milled Nb powder and Sn powder into the center tube. Then insert the mandrel, and the inlet and outlet wires of the niobium-tin superconducting wire pass through the wire grooves of the first and second lobes of the center tube, respectively, and pass through the wire grooves on the top surface of the mandrel and out of the center hole of the upper cover;

[0016] (4) Fix the base, rotate the upper cover, push the core shaft downward, pressurize the niobium-tin superconducting wire and the mixed powder of Nb powder and Sn powder in the central tube, and then maintain the pressure for 0.5h-2h;

[0017] (5) Rotate the upper cover in the reverse direction, release the pressure, and take out the niobium-tin superconducting wire and the joint of the superconducting wire;

[0018] (6) The niobium-tin superconducting wire is subjected to high-temperature heat treatment at a temperature of 650°C to 660°C.

[0019] The particle sizes of Nb powder and Sn powder are 100nm-500nm, and the molar ratio of Nb powder to Sn powder is 3:1.

[0020] The present invention makes an inlet and outlet line of a niobium-tin superconducting wire into a joint to form a closed loop, uses electromagnetic induction to react current in the joint loop, then tests the change of the magnetic field generated by the joint ring over time, and calculates the resistance of the joint according to the attenuation of the magnetic field.

[0021] The crimping die of the niobium-tin superconducting joint of the present invention can facilitate the operation of the niobium-tin superconducting wire with a fragile structure, and can protect the niobium-tin superconducting wire that is easily damaged during the process of making the joint. The crimping die of the niobium-tin superconducting joint of the present invention is used to make the niobium-tin superconducting joint, and after the Nb wire after corrosion at the end of the niobium-tin is mixed with the Nb powder and Cu powder after ball milling, the crimping die of the niobium-tin superconducting joint is used to apply pressure, and the pressure can be evenly loaded on the Nb wire and the mixed powder of the Nb powder and Cu powder, and the pressure is isotropic, and the pressure of each part is uniform, and no damage is caused to the superconducting wire and the Nb multi-filament. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the crimping die structure of the Nb-Sn superconducting joint;

[0023] Figure 2 Schematic diagram of the outer cylinder structure of the crimping die;

[0024] Figure 3 Schematic diagram of the cross-sectional structure of the outer cylinder of the crimping die;

[0025] Figure 4 Schematic diagram of the upper cover structure of the crimping die;

[0026] Figure 5 Schematic diagram of the central tube structure of the crimping die;

[0027] Figure 6 Schematic diagram of the mandrel structure of the crimping die;

[0028] Figure 7 Schematic diagram of the end of the Nb3Sn superconducting wire after corrosion. DETAILED DESCRIPTION

[0029] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0030] like Figure 1 As shown in FIG. 1 , the crimping die of the niobium-tin superconducting joint of the present invention comprises a base, an outer cylinder, a center cylinder, a core shaft and an upper cover. The base, the outer cylinder of the mold, the center cylinder, the core shaft and the upper cover are coaxial. The base is circular with a boss in the center, such as Figure 2 and Figure 3 As shown, the mold outer cylinder is mounted on the base, and the inner wall of the mold outer cylinder and the outer side of the boss of the base are fitted and fixed. There are pin holes on the bottom side of the outer cylinder, and the outer cylinder and the base are fixed by pins. The outer cylinder is mounted outside the center cylinder, and the core shaft is located in the center of the center cylinder. The upper cover is on the upper part of the mold outer cylinder, and the inner side of the upper cover has threads, such as Figure 4 As shown. The upper cover and the upper edge of the outer cylinder are threaded together to push the mandrel downward. The pitch of the thread is 0.5mm-1.5mm. A through hole is opened in the center of the upper cover for entering and exiting the niobium-tin superconducting wire. The upper cover is located vertically above the mandrel. During the downward rotation of the upper cover, the lower end surface of the top of the upper cover pushes the top surface of the mandrel, pushing the mandrel to move vertically downward.

[0031] like Figure 6 As shown, the core shaft is a T-shaped structure, a wire groove is opened on the top surface, and a positioning block is provided on one side of the cylindrical surface below the top surface.

[0032] like Figure 5As shown, the central tube is composed of three petals spliced ​​together to form a hollow cylinder. A wire groove is opened on each of the first petal 1 and the second petal 2 of the three petals. The two wire grooves are respectively located on the inner walls of the first petal 1 and the second petal 2, and are arranged symmetrically. The cross-section of the wire groove is circular, the radius of the wire groove is greater than the radius of the superconducting wire, and the depth of the wire groove is equal to the height of the first petal 1. The niobium-tin superconducting wire passes through the wire groove to prevent damage to the niobium-tin superconducting wire when it is subjected to force. There is a positioning groove on the inner wall of the third petal 3, and the positioning groove is on the same side as the positioning block of the core shaft. The positioning block on the core shaft is inserted into this positioning groove to position and guide the core shaft. There is a positioning block in the middle of the outer wall of the third petal 3. The positioning block is inserted into the positioning groove located on the inner wall of the outer tube, and cooperates with the positioning groove on the inner wall of the outer tube for positioning to prevent relative movement between the central tube and the outer tube.

[0033] Fix the outer cylinder and base of the mold horizontally, rotate the upper cover, and use the threaded fit of the upper cover and the outer cylinder to move the upper cover downward, pushing the mandrel below the upper cover to move vertically downward. During the movement, the positioning block on the side of the mandrel is inserted into the positioning groove of the center cylinder to ensure the linear movement of the mandrel without rotation. The lower end of the mandrel gradually presses the mixed powder of Nb powder and Sn powder in the center cylinder, so that the Nb wire at the bottom of the niobium-tin superconducting wire is pressed into one with the mixed powder of Nb powder and Sn powder.

[0034] The working process of the crimping die of the present invention for crimping the niobium-tin superconducting joint is as follows:

[0035] (1) A superconducting wire is wound into one or more turns, with the two ends of the superconducting wire aligned side by side as the inlet and outlet ends. Figure 7 As shown, nitric acid is used to corrode the copper at the inlet and outlet ends of the Nb3Sn superconducting wire, and the length of the corrosion section is 0.5cm-10cm, exposing the Nb multifilaments and the support core in the Nb3Sn wire, and the support core is removed;

[0036] (2) Mix the Nb powder and Sn powder and then ball mill them for 5h-20h. The particle size of the Nb powder and the Sn powder is 100nm-500nm. The molar ratio of Nb powder to Sn powder is 3:1. Insert the two ends of the niobium-tin superconducting wire vertically into the central tube from the wire grooves of the first lobe and the second lobe of the central tube on both sides, respectively. The uncorroded part of the niobium-tin superconducting wire reaches the upper surface of the base boss, and the Nb multifilament enters the central tube. Pour the ball-milled Nb powder and Sn powder into the central tube. Then insert the core shaft, and the input and output wires of the niobium-tin superconducting wire pass through the wire grooves of the first lobe 1 and the second lobe 2 of the central tube respectively, and pass through the wire grooves on the top surface of the core shaft from the center hole of the upper cover;

[0037] (3) Fixing the base, rotating the upper cover 1 to 10 times, driving the core shaft to move downward, pressurizing the niobium-tin superconducting wire and the mixed powder of Nb powder and Sn powder, and maintaining the pressure for 0.5h to 2h;

[0038] (4) After the pressure is maintained, the upper cover is rotated in the opposite direction, and after the pressure is released, the base is removed, and the central tube is taken out from the bottom. Then, the three petals of the central tube are separated, and the niobium-tin superconducting wire and the superconducting joint are taken out;

[0039] (5) The niobium-tin superconducting wire and the superconducting joint are subjected to high-temperature heat treatment at a temperature of 650°C-660°C.

Claims

1. A crimping die for a niobium-tin superconducting joint, characterized in that: The crimping die is a cylindrical structure, including a base, a die outer cylinder, a center cylinder, a core shaft and an upper cover, and the base, the die outer cylinder, the center cylinder, the core shaft and the upper cover are coaxial; the base is circular, with a boss in the center, and a pin hole on the side of the boss; the die outer cylinder is sleeved on the base, and the inner wall of the die outer cylinder and the outer side of the boss of the base are fitted and fixed; there is a pin hole on the side of the bottom of the outer cylinder, and the outer cylinder is fixed to the base by a pin; the outer cylinder is sleeved outside the center cylinder, and the core shaft is located in the center of the center cylinder; the upper cover is on the upper part of the die outer cylinder, and the inner side of the upper cover is threaded, which cooperates with the upper edge of the die outer cylinder through the thread, so that the upper cover pushes the core shaft to move downward; a through hole is opened in the center of the upper cover for entering and exiting the niobium-tin superconducting wire; the upper cover is located directly above the core shaft, and during the downward rotation of the upper cover, the top lower end surface of the upper cover contacts the top surface of the core shaft, pushing the core shaft to move downward; The central tube is a hollow cylinder formed by splicing three petals; a wire groove is respectively opened on the inner wall of the first petal (1) and the second petal (2) of the three petals, the cross section of the wire groove is circular, the radius of the wire groove is greater than the radius of the niobium-tin superconducting wire, and the depth of the wire groove is equal to the height of the first petal (1); the niobium-tin superconducting wire passes through the wire groove; a positioning groove is provided in the middle of the inner wall of the third petal (3), and a positioning block on one side of the core shaft is inserted into the positioning groove for positioning and guiding the core shaft; a positioning block is provided in the middle of the outer wall of the third petal (3), and the positioning block is inserted into the positioning groove located on the inner wall of the outer tube of the mold, and cooperates with the positioning groove on the inner wall of the outer tube for positioning, so as to prevent relative movement between the central tube and the outer tube.

2. The crimping die for the niobium-tin superconducting joint according to claim 1, characterized in that: The mandrel is a T-shaped structure with a wire groove on the top surface; a positioning block is provided on one side of the cylindrical surface below the top surface of the mandrel.

3. The crimping die for the niobium-tin superconducting joint according to claim 1, characterized in that: The pitch of the thread on the inner side of the upper cover and the upper edge of the outer cylinder of the mold is 0.5mm-1.5mm.

4. The crimping die for the niobium-tin superconducting joint according to any one of claims 1 to 3, characterized in that: When the crimping die is working, first the base is fixed horizontally, the upper cover is rotated, and the upper cover is moved downward by using the threaded cooperation between the upper cover and the outer cylinder of the die, so as to push the core shaft below the upper cover to move vertically downward; during the movement, the positioning block on the side of the core shaft is inserted into the positioning groove of the center cylinder to ensure the linear movement of the core shaft without rotation; the lower end of the core shaft gradually presses the mixed powder of Nb powder and Sn powder in the center cylinder, so that the Nb wire at the bottom of the niobium-tin superconducting wire is pressed into one with the mixed powder of Nb powder and Sn powder.

5. The crimping die for the niobium-tin superconducting joint according to claim 4, characterized in that: The specific process of preparing superconducting joints by the crimping die is as follows: (1) Winding a superconducting wire into one or more turns, with the two ends of the superconducting wire aligned side by side as the inlet and outlet ends; corroding the copper layer at the inlet and outlet ends of the niobium-tin superconducting wire with nitric acid, with the corrosion section length of 0.5 cm to 10 cm, exposing the Nb multifilaments and the support core in the niobium-tin superconducting wire, and removing the support core; (2) mixing Nb powder and Sn powder and then ball milling for 5 h to 20 h; the particle size of Nb powder and Sn powder is 100 nm to 500 nm, and the molar ratio of Nb powder to Sn powder is 3:1; (3) The two ends of the Nb3Sn superconducting wire are respectively inserted vertically into the central tube through the wire grooves of the first lobe (1) and the second lobe (2) on both sides of the central tube, so that the uncorroded part of the Nb3Sn superconducting wire reaches the upper surface of the base boss and the Nb multifilament enters the central tube; the ball-milled Nb powder and Sn powder are poured into the central tube; then the mandrel is inserted, and the inlet and outlet wires of the Nb3Sn superconducting wire pass through the wire grooves of the first lobe (1) and the second lobe (2) of the central tube respectively, and pass through the wire grooves on the top surface of the mandrel and out of the center hole of the upper cover; (4) Fix the base, rotate the upper cover, push the core shaft downward, pressurize the niobium-tin superconducting wire and the mixed powder of Nb powder and Sn powder in the central tube, and then maintain the pressure for 0.5h-2h; (5) Rotate the upper cover in the opposite direction, remove the base after depressurization, remove the central tube from the bottom, and then separate the three petals of the central tube to remove the niobium-tin superconducting wire and its superconducting joint; (6) The niobium-tin superconducting wire and its superconducting joints are subjected to high-temperature heat treatment at a temperature of 650°C to 660°C.

6. The crimping die for the niobium-tin superconducting joint according to claim 4, characterized in that: The number of revolutions of the upper cover is 1 to 10.

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